Phase-shifting network



Feb. 17 1931.

PHASE SHIFTI NG NETWORK Filed March 12, 1927 Phase Shift (flag/'26s) 10 2'0 30 40 5b 6b INVENTOR.

IfZlocycles/Sec. 0 J Z 06 e6 ATTORNEY 45 shown in Figs. 2 toe, inc'lusiv c The phaseshifting networks in which the invention is embodied are ofthe lattice type,

Patented. Feb. 17, 1931 UNITED; STATES PATENT OFFICE OTTO T. ZOBEL, OF NEW YORK, N. Y., ASSIGNOR T AMERICAN TELEPHONE AND TELE- GRAPH COMPANY, A CORPORATION OF NEW YORK PHASE-SHIFTING NETWORK Application filed March 12, 1927. SeriaINo. 174,984.

This invention relates to phase shifting 10 the phase of the current in a part of the systern in order to bring it into phase or in opposition to the current inanother part ofthe;

system. Thus, for example, in a radio receivlng system, employing a plurality of antonnes, directional selectivity is produced by varying the phase offthe current in one antenna so that it will oppose the current fromv the same source produced in the other antenna, thus, effectively balancing out an un- 2 desired signal or-other source of interference.

My invention resides in a phase shifting network having a constant characteristic impedance, negligible attenuation, and phase constants which, over the desired frequency range, are very accurately proportional to I frequency.

, The invention will be clearly understood Y from the following description when read in connection with the attached drawing of which'Figure 1 shows animpedance network of the lattice type representing aninfinite number of elements andhaving a constant characteristic impedance,the said figure illustrating the description of the underlying principle upon which the invention is based Fig. 2 represents a network of the one parameter type, which network inayiemploy either fixed units or variable units, in which case thephase shift may bevaried through a pre- .40 determined range of values; .Fig. 3 is a network of two parameter type; Fig tis a composite network of the threeparameter type and Fig. 5Lare characteristic curves repre-.

senting the characteristics of'the networks being either single sections or composite sections- The general form ofnetworkof single section type having a constant impedance B is illustrated in Fig. 1 and the propagation constant of that network is given by L JZM *1;- a /2R (11) Where z z fi i In Fig.1,- z representsthe total series impedance of the network and z represents the total lattice impedance. 'The series"imped ance is represented as being equally divided between the twosides of'the circuit, each half having a value 2 /2. In order that the total lattice impedance shall equal z 'each shunt unit has the'value2a a It will be remembered that if we terminate a plurality of networks inseries, each of the'types shown in Fig. l, byan impedance--R, the impedance looking into the opposite end of the-said plurality of networks will equal R.

The derivation of the'formulae for the different sections will-nowbeshown, the number of parameters corresponding to the number of different series elements involved.-

Onejparameter lattice; M

In this network, which is shown in Fig. 2,

. the series elements is an inductance L which is preferably uniformly distributed between the two sidesof the circuit in order to maintain a balanced condition. The lattice ele ments are the condensers C 7 z 1 f v r where v 7 f=frequency V g=1rLi1/R, and L =gR/7r==L 7 Substituting in equation (1), the value for V 2R given by (2) equation (1 )b ecomes V 1+'z:fg

Substituting for I its equivalent A+iB V H .1+jg

A iB e i f f which when multiplied by Since 0 then the above becomes 1+f g +t (f 1/ 1 H 9 #1 H 9 tan=fg or G=P-f 3 where B is the phase constant, G is introduced for convenience, and P g.

If at f=f 3 19 then P=G /f (4) In the notation of Fig. 2,

Two parameter lattice In this network, which is shown in Fig. 3,

the total series element is an anti-resonant in ductance L and capacity 0 /2. The lattice elements are resonant paths each made up of an inductance 11 /2 in series with a capacity 1,. As will be seen where Three parameter composite lattice This network, shown in Fig. l, is made up of one each of the two preceding sections. For this composite section the phase constant is given from (1), (2), and ((3) by 1 f 1 ifg'1 ?jhf m with the same meanings attached to g, 171), and

m as above. Theme,

Where 8 gm, all positive.

From (11) follows the linear relation PifG Q -S'= G/;. (12) Fixing the phase at three frequencies determines these coeliicients P, Q, and S. The relations between g, h, m and the fm'mer are the following:

g Pg (3 -5 0,

from which cubic /3 c\/b +e The general equations set forth hereinbefore, for the one, two, and three parameter networks, will now be applied to the design of phase shifting networks having specific values, the purpose of which application is to more fully describe the invention.

Let it be assumed that the requirements to be met by the networks are as follows: (a) a constant characteristic impedance of F. equal to 600 ohms; (b) a continuously varied phase shift which is proportional. to frequency through the frequency range from 50 to kilocycles per second, the total phase shift range being from zero to 250 degrees at 50 kiloc-ycles per second; (0) over any frequency band of 5 kilocycles per second in the range set forth in (b), the variations should be less than 1/10 degree for the phase and less than -.025 TU or the attenuation; and 1:25

where to 15 degree continuously variable section v This section has one parameter which at any frequency is determined from (3) and (4) and the elements from (5). The inductances and capacities, L and C must be ad- 1 Justable over a continuous range and have the magnitude-phase characterlstics contamed 1n the followlng relations between inagniture and phase at 50,000 cycles/sec.

11 3g;- =r io 01 (m) 50,000 0 0 0 0 50, 000 1 0174 times 10 0332 0401 times 10 50, 000 2 0350 times '10 0660 0928 times 10 50, 000 3 0524 times 10 1001 1390 times 10 2 50,000 4 .0698 times 10- .1333 .1351 times 10- 50, 000 5 0874 times 10" 1669 2318 times 10 00, 000 6 1048 times 10 2002 2779 times 10- 50, 000 7 1224 times 10 2338 3240 times 10 50, 000 8 1398 times 10 2670 3707 times 10 50, 000 9 1574 times 10 3000 4174 times 10 50, 000 10 1750 times 10* 3342 4641 times 10' 50,000 11 1926 times 10 3079 5108 times l0- 50, 000 12 2102 times 10 4015 5574 times 10 50, 000 13 2278 times 10 4351 i 6041 times 10 )0, 000 14 2456 times 10' 4691 0513 times 10 50, 000 15 .2634times 10f 5031 6985 times 10 IO-clogre section This one parameter section has the constants corresponding at f 50,000 to B 10 degrees, as above. g g

ZO-degree section 50,000 3 20.00 degrees 7 f 65,000 7 B =26.'00 degrees P h 341907-10 Q =m=. .0407 07 10- L .6667mh. 0 .309310 m7. 0* .9259-10 mf. L .22272mh.

45 r {LO-degree section f 50,000 3 :40.00 degrees f 65,000 B 52.00 degrees P=h=.69774l-10' Q=m=.16595-10' 9 L 1.333mh. (7 0309-10 0127.

0 Lem-10%;".

V SO-dogree section .7625-10' L 121117170. 0 L682-10 mftermined frequency range. factor of proportionality Jed-degree section i B =160.00 degrees f 57,500 B 184.00 degrees I f 65,000 V g B =208.00 degrees P=2.830S-10? LS: 1.80 l0-10 Q=.1603-10' Whilethe Variable section is normally requn-edto give a'maxlmum of but 10 degrees, an extension 0t this range to 15 degrees has i been made to insure phase overlapping at any transition point Where a section having a fixed value is put into or taken out of the circuit. By combining these sections, a continuous range of from zero to 325 degrees obtainable. The attenuation requirements are-met by choosing coils having a small diss-upaiiion constant 6!. p v

I An idea or the accuracy of the phase shifting networks, described hereinbeforc,

may be derived from the following table which sets forththe departure in degrees i of phase for the various frequencies between 50 and 65 kilocycles. Phase depdrtnres (degrees) from ideal proportionality throughthe range from 50 to 65kilocycles v v The proportionality of the phase shift to frequency is shown clearly' by Fig. 5. All of the curves shown thereon pass through the origin. Furthermore, it will be apparent from an inspection of the curves of Fig. 5 thatthe factor of proportionality for each section remains constant through a prede- The. expression means the ratio B 7 ithat'is to say, the slope of the characteristic.

. lVith regard to the feature of resonance, Which is presented by Figs. 3 and 4: it is desirable to point out that the resonant free 'quency of these networks will be Well outside and also as embodied in combinations of those sections, it will be apparent that the V invention may be embodied in sections having other forms and other combinations of sections Without departing from the spirit and scope of the appended claims.

hat is claimed is:

1. A phase shifting network comprising two subsidiary networks serially connected, one 01" said networks comprising series inductance and lattice connected capacity and having a constant characteristic impedance, and the other of said networks comprising series elenien 's each consisting of inductance and capacity that anti-resonant, and lattice connect-ed elements each consisting of reson ant inductions and capacity, the product of the series and lattice branches of said other network being constant with respect to frequency and the said network having a constant characteristic impedance.

2. A phase shifting network comprising series elements each consisting of inductance and capacity which are anti-resonant, and lattice connected elements each consisting of resonant inductance and capacity, the product of the series and the lattice branches being constant with respect to frequency, and the said network having a constant characteristic impedance.

In testimony whereof, l have signed my name to this specification this 11th day oi? March, 1927.

OTTO .l ZOBEL. 

